66 mustang engine needed

Sorry for posting FERD stuff here but, My father-in-law is at his rope ends. I just spent 3 days helping install a 170 ci straight six in his daughters 66 mustang. He got it from a "freind" that said it ran when pulled. Well, it ran for about 10 minutes and locked up. Does anyone have good resources for a 200 straight six? I can get a long block rebuild from autozone for 1 thousand plus core but would like to help him save some money. He is a Vet on fixed income. He only has about 500 for the engine. Anything above that is coming from my pocket just to help him out. Anyone got any ideas?